Short-wave permeability tuning system



March 11, 1947. w. F. SANDS SHORT-WAVE PERMEABILITY TUNING SYSTEM Filed Oct. 24, 1942 2 Sheets-Sheet. 1

INVENTOR.

BY W/u/AM F SQ/v05.

ATTORNEY Patented Mar. 11, 1947 SHORT-WAVE PERMEABILITY TUNING SYSTEM William Francis Sands, West-Collingswood, N. J., assignor to Radio Corporation of America, a

corporation of Delaware Application October 24, 1942, Serial No. 463,192

11 Claims. 25040) My present invention relates to a variable permeability tuning system for short-wave superheterodyne receivers, and more particularly to the core and coil structure utilized in the signal frequency and oscillator circuits of such receivers for efiecting tracking between said circuits.

It is one of the objects of my invention to provide an improved variable permeability tuning system for causing the oscillator and signal input circuits to track accurately one with the other throughout a predetermined frequency range.

There are several known methods and means for effecting tracking in the tuning of two or more circuits by variable permeability tuning means, some of which are impracticable because of cost or manufacturing difficulties, and others of which are adaptable for commercial application. As an instance of the latter there is described and claimed in my Patent No. 2,255,680, issued September 9, 1941, a permeability tuning system utilizing coils of d-ifierent diameters for the signal frequency and oscillator circuits.

As an improvement over certain of the latter systems, I have determined that two or more vari-' able permeability tuned circuits may be caused to tune through different frequency ranges with accurate tracking by using the same diameter coils.

It is therefore an object of the present invention to provide tracking at a plurality of points of the tuning range with the use, in a superheterodyne receiver, of radio frequency and oscillator coils having the same diameter coil forms and tuning cores which are substantially of the same structure or'geometry. 4

It is also an object of the present invention to provide an improved tuning system for a superheterodyne receiver which provides for the alignment of and a desired tracking relation between two or more tuna=blecircuits at a plurality of points in the tuning'rangef It 'is a further object of the invention to provide an oscillator tuning inductance which is similar to the tuning inductance of the signal frequency circuit except for. the Winding pitch or turns-per-inch and which is adapted for causing alignment or tracking of the oscillator circuit with the signal frequency circuit at a plurality of points in a predetermined frequency range.

The invention will be further understood how- 50 ever from th following description, when considered in connection with the accompanying drawings and its scope is pointed out in the appended claims.

In the drawings,

of a portion of the cirelements shown in either Figs. 1 and 1a,

Fig. 3 are curves showing the relationbetween tuning range and winding pitch of a plurality of inductance coils differing only in the winding pitch,

Fig. 4 is a curve showing the relation between the effective permeability and the turns-perinch for the same coils, and

Fig. 5 is a graph showing curves illustrative of the tracking relation between th two circuits shown in Fig. 1. 7

Referring now to Fig. 1, the tuning system of the receiver is shown to comprise a tunable signal input circuit 1 coupled to the signal grid of a, combined detector-oscillatortube '2. The signal input circuit includes a variable permeability tuned inductance 3 shunted by suitable capacity means and-a movable tuning core 4. The frequency-determining circuit 5 of the oscillator, shown as of the Colpitts type, comprises a variable permeability tuned inductance 6 coupled to the first grid of the tube [and provided with a movable tuning core 1, and suitable shunt capacity means 8 and 9, the common terminal of which is connected to the cathode of tube 2. The two movable tuning cores 4 and l are adapted for uni-control operation as indicated by-the dash line connected therebetween. v

The signal input circuit I is connected at its high potential side to any suitable signal source,

such as an antenna A through a suitable coupling capacitor l0. Instead of the signal source feeding directly to the input circuit l of the detector-oscillator, there may be interposed therebetween a stage of radio frequency amplification, as welliknown in the art, in which case said stage will be provided witha signal input circuit similar to the circuit 1, and its movable core would alscbe mechanically coupled to the tuning .cores 4 and l. Signals of intermediate frequency are derived from the detector-oscillator through a suitable tuned intermediate frequency coupling transformerT the primary of. which'is connected in the output thereof.

The coil structure, of the signal frequency and oscillator circuits is shown in Fig. 2 in which the same reference numerals are used to designate like parts as in Fig. '1. The signal frequency coil I 56 3, and the oscillator coil 6 which are wound with termediary of adjusting screws 15 and the operating rods Suitable means such as a control knob 16 at the end of a screw shaft 11 which is in threaded engagement with an internally threaded bushing 18 ailixed to the carriage serves to move the tuning cores to any desired position of adlustment.

I have determined by calculation and experimentation that it is possible to secure the proper tuning range for a short-wave permeability tuned oscillator circuit by employing the change in effective permeability (,lLe) due to varying the turns-per-inch (T. P. I.) of the winding. This effect is particularly pronounced for windings below 50 T. P. I. and may be used whether the oscillator is above or below the signal frequency. In Fig. 3 several curves are shown which represent the respective tuning ranges of coils having the same diameter wire and coil length but different, winding pitch. It will be observed that as the winding pitch is increased, the tuning range is increased. Thus, for example, for a coil with a pitch of 5.7 turns-per-inch, the tuning range is from 18 mo. with the core just entering the coil to 11.9 mc. with the core fully entered into the coil; and for a coil with a pitch of 27.2 turns-per-inch the tuning range as determined by the core travel noted above is from 18 to 7.8 mc., an increase of over 4 mc. or 66%.

In Fig. 4 there is shown a curve which gives the change in effective permeability (lie) for coils of the same geometry but with differing T. P. 1. Each point on the curve represents the square of the individual tuning ranges, i. e, (f1/f2) ;,ue for the various curves asshown by Fig. 3.

Let us consider a required range of 8 to 18 mo. with an I. F. of 4,55 kc. Let fs=signal frequency, and jo==oscillator frequency. The frequency range, the ratio of the limiting frequencies, and the effective permeability for the signal frequency circuit and the oscillator circuit when tuned above and below the signal frequency are given below:

eq e y range fl o 1'2 Range =f1/fz (fl/f2) r.=1s to 8 me 2. 25 5.06 t -f.+l.

=l8.455=l7.545 (f 2, 353 5. 53

It will be seen that for the given coil geometry and cores which result in Fig, 4, the pitch for the signa1 frequency coil which will give the required tuning range, corresponding to /J.e=5.06, as calculated, is 22 T. P. I. For operation of the oscillator at a frequency above the signal frequency, a pitch of 18.5 T. P. I. will give the correct oscillator tuning range, correspondin to Me=4.76. Similarly, for oscillator operation at a frequency below the signal frequency a pitch of 34 T. P. I. is seen to be required to cover the tuning range corresponding to ,lte =5.53.

,By utilizing differently pitched coils as deter-. mined in the manner above described, and--with-- out the use of additional series or shunt inductances, there will be obtained two point tracking between the signal frequency and oscillator circuits. However, three point tracking may be produced by the use of an adjustable capacitor 19 (Fig. 1) shunted across a tapped portion of the ground end of the oscillator coil 6, as disclosed in the patent to V. D. Landon, No. 2,248,242. In the particular circuit disclosed in Fig. 1 a single tap at 6 turns, shunted by a 15-150 as trimmer type capacitor was used. With the use of additional taps and shunt capacitors, one being shown at 20, further crossover points may be obtained. In Fig. 5 there are shown the. curves for the alignment between the signal frequency and the oscillator coils using the present invention in conjunction with capacitors l9 and 20 of Fig. 1. Curve I is the signal frequency curve for a frequency range between 16.5 and 8.5 mc. Curve 2 is the desired oscillator tuning curve spaced from curve I a distance corresponding to 455 kc., the value of the intermediate frequency,.and curve 3 is the final oscillator alignment that was secured.

In the circuit of Fig. 1 the tuning system was described as of the continuously variable type, that is, the tuning range is covered by a full stroke movement of the tuning cores from a position where they just enter the respective coils to a position where they are fully entered therein, tuning to a particular frequency being accomplished by movement of the cores to an intermediate position. However, in a system where it is desired to eifect band-spread tuning by means of an auxiliary series-connected coil according to the method described in my application, Ser. No. 463,193, filed concurrently herewith, the presence of said coil serves to somewhat reduce the available range, so that in this case the turns per inch required for the main oscillator coil would be different from the case where no auxiliary coil is used. In Fig. 1a there is shown themodiiied oscillator circuit 5' which may be substituted for the circuit 5 in Fig. 1

- to the right of the line aa. The auxiliary or band-spread coil is shown at El being serially connected at the high potential end of the main oscillator coil 5. The core I of the latter is adapted for adjustment to a fixed predetermined position while the core 22 of the auxiliary core is adapted for continuous adjustment for efiecting band-spread-tuning of the receiver. The actual pitch of the oscillator coil 6 for this case compared to that of the signal frequency coil 3 will depend upon theefollowing factors: (1) the signal frequency range f1fz), (2) the intermediate frequency, (3) themagnitude of the band spreading coil 2l compared to the main oscillator coil 6Q and (4) the extent of the spread bands. -'l-herefor e, the final oscillator coil pitch must be determined somewhat empirically, using the curves-of Figs. 3 and for guidance in the design. It' will be noted that fora parample, utilizing a 26 turn coil oft- 32 en. wire, the

tuning range was found to extend fromlB to 8.16

mc., with a full stroke movement of the core, whereas a coil having a similar number of turns and a larger wiresize of #21 en. was found to have a tuning range extending from 18 to 7.96 mc., an increaseof 0.2.mc.

The reason for this may be explained by the fact that with an increase in the wire diameter, the actual number of turns being held constant, the distance between turns is decreased thereby resulting in a slightly larger effective permeability for the coil and core system, and with a decrease in wire diameter, the distance between turns is increased thereby resulting in a slightly decreased effective permeability for the coil and core.

What I claim is:

1. In a permeability tuning system for a superheterodyne receiver, a signal frequency circuit and an oscillator circuit each having a tuning coil and a magnetic tuning core movable relatively to said coil to inductively tune its respective circuit, said tuning cores :being of substantially the same length and diameter, said tuning coils being of like construction as regards coil length and coil diameter but having different winding pitches which are constant in each case, the relative pitches of said-coils being so chosen as to effect substantially constant trackin between said circuits with synchronous adjustment of the cores through their respective tuning ranges.

2. In a permeability tuning system for a superheterodyne receiver, a signal frequency circuit and an oscillator circuit each having a tuning coil and a magnetic tuning core movable relatively to said coil toinductively tune its respective circuit, said tuning cores being of substantially the same length and diameter, said coils being of like construction as regards coil length and coil diameter, the coil of the oscillator circuit having a larger winding pitch than that of the signal circuit and being so chosen that substantially constant tracking is established between said circuits with the synchronous adjustment of their associated cores through their respective tuning ranges.

3. In a permeability tuning system for a superheterodyne receiver, a signal frequency circuit and an oscillator circuit each having a tuning coil and a magnetic tuning core movable relatively to said coil to inductively tune its respective circuit, said tuning cores being of substantially the same length and diameter, said coils being of like construction as regards coil length and coil diameter, the coil for the oscillator circuit having a smaller winding pitch than that of the signal circuit and being so chosen that substantially constant tracking is established between said circuits with the synchronous adjustment of their associated cores through their respective tuning ranges.

4. In. a variable permeability tuning system, the combination of two inductance coils included in circuits which are tunable through different frequency ranges, a powdered iron tuning core movable within its respective coil, said cores being of substantially the same length and diameter, said coils being wound each on a coil form of the same diameter and with its turns uniformly spaced, one of said coils having a fewer number of turns per inch than the other thereby causing a decrease in the effective permeability thereof, so that a predetermined tracking relation is provided in the tuning response of said coils with synchronous tuning movement of said cores.

5. In a variable permeability tuning system for a superheterodyne receiver, the combination 6 of two inductance coils each having a movable powdered iron tuning core, said cores being of substantially the same length and diameter, said coilsbeing woundeach-on a coil form of the same diameter and with its turns uniformly spaced, one of said coils being included in the oscillator circuit and having a fewer number of turns per inch than the other coil which is included in the signal frequency circuit, thereby causing a decrease in the efiective permeability of said oscillator circuit coil, so that a predetermined tracking relation is provided in the tuning response of said circuits with synchronous tuning movement of said cores.

6. In a variable permeability tuning system, the combination of a pair of tuning inductance coils included in a pair of circuits which are tunable through different frequency ranges, a pair of powdered iron tuning .cores movable each within its respective coil, said cores being of substantially the same length and diameter, said coils being wound each on acoil form of the same diameter and with its turns uniformly spaced, said cores being interconnected for synchronous control of the tuning of said circuits, and means for causing a decrease in the effective permeability of one of said coils thereby to efiect tracking in the tuning response of the circuit of said coil with respect to that of the circuit of the other coil, said means being constituted by a winding pitch for said one coil which differs from the winding pitch of said other coil.

7. In a variable permeability tuning system for a short-wave superheterodyne receiver, a signal frequency circuit and an oscillator circuit, a tuning inductance coil and a movable tuning core for each of said circuits, said cores being of substantially the same length and diameter, said coils being wound each on a coil form of the same diameter and with its turns uniformly spaced, said cores being interconnected for synchronous control of the tuning of said circuits, and means for causing a decrease in the effective permeability of the oscillator circuit coil thereby to effect tracking in the tuning response of said oscillator circuit with respect to the signal frequency circuit, said means being constituted by a winding pitch for said oscillator coil which differs from the winding pitch of the signal frequency coil.

8. In a variable permeability tuning system, the combination of apair of tuning inductance coils of substantially the same diameter and coil length, said coils being included in different circuits which are tunable through different frequency ranges, a pair of tuning cores of substantially the same length and diameter movable each within its respective coil, said cores being interconnected for synchronous control of the tuning of said circuits through their respective frequency ranges with the same length of travel of said cores, and means for causing a decrease in the eifective permeability of one of said coils thereby to effect tracking in the tuning response of the circuit of said latter coil with respect to that of the circuit of the other coil, said means being constituted by a winding pitch for said one coil which differs from the winding pitch of said other coil, and shunt capacitor means connected across one or more tapped portions of one of said coils.

9. The combination defined in claim 8 wherein the shunt capacitor means is connected across one or more tapped portions of the coil having the smaller winding pitch.

10. The combination defined in claim 8 wherein the shunt capacitor means is connected across one or'more tapped portions of the coil having the larger winding pitch.

11. In a variable permeability tuning system for a short-wave superheterodyne receiver, the combination of a pair of tuning inductance coils of 5 substantially the same diameter and coil length, one included in the oscillator circuit and the other in the signal frequency circuit, each coil having a movable tuning core of substantially the same length and diameter, said cores being interconnected for synchronous control of the tuning of said circuits through their respective frequency ranges with the same length of travel of said cores, and means for causing a decrease in the effective permeability of the oscillator circuit coil thereby to effect tracking in the tuning response of said oscillator circuit with respect to that of the signal frequency circuit, said means being constituted by a winding pitch for said oscillator coil which is smaller than the winding pitch of the signal frequency coil, and shunt capacitor means connected across one or more tapped portions of the oscillator coil.

WILLIAM FRANCIS SANDS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,082,595 Polydorofi June 1, 1937 2,095,420 Polydorofi Oct. 12, 1937 2,259,250 Jacob Oct. 14, 1941 2,289,670 McClellan July 14, 1942 2,301,934 Edwards Nov. 17, 1942 2,255,630 Sands et a1 Sept. 9, 1941 2,344,091 Kirk Mar. 14, 1944 2,310,720 Wandrey Feb. 9, 1943 2,330,833 Marholz et a1 Oct. 5, 1943 2,252,092 Newman Aug. 12, 1941 2,248,242 Landon July 8, 1 1 2,222,387 Wheeler et al Nov. 19, 1940 ,2 3,613 Conron Nov. 25, 1941 FOREIGN PATENTS Number Country Date 447,104 British May 12, 1936 

